Biomedical subjects

Leif Sörnmo

Publications and source records attributed to Leif Sörnmo.

At least 19 recordsLinked to original sources

PubMed2007

Validation and clinical application of time-frequency analysis of atrial fibrillation electrocardiograms.

INTRODUCTION: Fibrillatory rates can reliably be obtained from surface ECGs during atrial fibrillation (AF) and correspond with right atrial (RA) and coronary sinus (CS) rates, while both the relation with pulmonary venous (PV) rates and determinants of fibrillatory waveform are unknown. Class III antiarrhythmic drugs prolong atrial refractoriness and decrease its dispersion, effects that may be reflected in ECG parameters. Consequently, this study sought (1) to investigate the relation between ECG fibrillatory rate and waveform characteristics with intraatrial/PV fibrillatory activity and (2) to noninvasively monitor class III antiarrhythmic drug effects in patients with AF. METHODS AND RESULTS: Thirty-six patients with drug-refractory AF who underwent catheter-based pulmonary vein isolation and had AF at the beginning of the procedure were studied. A positive correlation between V1 rates obtained by time-frequency analysis and RA (R = 0.97, P < 0.001), CS (R = .71, P < 0.001), and PV rates (R = 0.65, P = 0.001) was found. Exponential decay defined as decay of the curve that connects power maxima of dominant and harmonic frequency components correlated with RA rate dispersion (R = 0.53, P = 0.004). In amiodarone-treated patients (n = 7), V1 rate (286 +/- 64 vs. 371 +/- 40 fpm, P < 0.001) and exponential decay (1.06 +/- 0.29 vs. 1.38 +/- 0.38, P = 0.034) were lower than in patients without amiodarone (n = 29). In 19 additional patients with persistent AF, oral dofetilide treatment decreased mean fibrillatory rate from 377 +/- 57 to 294 +/- 50 fpm (P < 0.001) and exponential decay from 1.24 +/- 0.43 to 0.85 +/- 0.22 (P = 0.002). CONCLUSIONS: Fibrillatory waves of surface ECG lead V1 closely reflect right atrial, and, to a lesser degree, left atrial activity. Time-frequency analysis allows noninvasive monitoring of antiarrhythmic drug effects on fibrillatory rate and waveform.

Anti-Arrhythmia Agents↗

PubMed2006

Electroatriography - time-frequency analysis of atrial fibrillation from modified 12-lead ECG configurations for improved diagnosis and therapy.

Current atrial fibrillation (AF) management guidelines suggest that initially a decision must be made to apply either a rate control or rhythm control strategy in the individual patient. However, patients' selection remains substantially empirical and the strategy initially chosen often proves unsuccessful and alternative therapies must be adopted. Thus, it seems desirable to develop and apply tests that quantify AF disease state and guide AF management. The overall hypothesis of this paper is that time-frequency analysis of AF from modified 12-lead ECG configurations will improve AF management beyond current diagnostic and therapeutic standards. In particular, we present a novel concept in which 12-lead ECG configurations are modified for time-frequency analysis of AF (electroatriography). While five electrodes (VR, VL, VF, V1, V2) are placed in the conventional position, the other four electrodes (V3, V4, V5, V6) are empirically repositioned anterior or posterior over the atria. By applying spatiotemporal QRST cancellation and time-frequency analysis to these recordings in 19 patients with persistent AF, fibrillatory rate dispersion among individual anterior (25+/-14 fibrillations per minute, fpm) and posterior leads (16+/-11fpm) as well as individual anterior/posterior rate gradients ranging between -24 and +116fpm could be identified. Consequently, the portrayed techniques may form the conceptual basis for individualized noninvasive characterization of AF. Initiation of further studies using the described techniques in different AF subsets, for comparisons with intracardiac recordings and outcome of different therapies, e.g. cardioversion, antiarrhythmic drug and ablation therapy may be stimulated.

Aged↗

PubMed2006

Assessment of QT-measurement accuracy using the 12-lead electrocardiogram derived from EASI leads.

The purpose of the present study is to assess QT-interval measurements from the EASI 12-lead electrocardiogram (ECG) as compared with the standard 12-lead ECG. The QT interval was automatically determined in simultaneously recorded standard and EASI 12-lead ECGs, using a validated wavelet-based delineator. The agreement between the 2 sets of measurements was quantified both on a lead-by-lead basis and a multilead basis with global definitions of QRS onset and T-wave end. The results show that the agreement between QT-interval measurements from the 2 lead systems is acceptable, with negligible mean differences and with correlation coefficients ranging from 0.91 to 0.98 depending on the lead studied. Although the SD shows a clear dependence on the selected lead (ranging from 9.2 to 26.4 milliseconds), differences are within the accepted tolerances for automatic delineation. In a few patients, large differences were found, mainly because of changes in morphology present in both lead systems. QT intervals measured by the multilead approach were considerably more stable than single-lead measurements and resulted in a much better agreement between the 2 lead systems (correlation coefficient, 0.98; QT difference, 1.1 +/- 9.8 milliseconds). Thus, the EASI 12-lead ECG may be used for reliable QT monitoring when the multilead delineation approach is adopted.

Diagnosis, Computer-Assisted↗

PubMed2006

Atrial fibrillatory rate and sinus rhythm maintenance in patients undergoing cardioversion of persistent atrial fibrillation.

AIMS: The study set out to explore whether an index of atrial electrical electrophysiology can be used to predict atrial fibrillation (AF) relapse, and if the predictive properties differ as a result of arrhythmia duration. METHODS AND RESULTS: The study comprised 175 consecutive patients with persistent AF (median duration 94 days, range 2 to 1044) referred for cardioversion. Twenty-nine patients had arrhythmia duration under 30 days (median 5 days, range 2-26). Atrial fibrillatory rate (AFR) was estimated using a frequency power spectrum analysis of QRST-cancelled ECG. At 1-month follow-up, 56% of the patients had relapsed to AF. The pre-cardioversion mean AFR of those patients was 399+/-52 fibrillations per minute (fpm) compared with 363+/-63 fpm among patients maintaining SR (P<0.0001). In patients with short AF duration, the difference was even more pronounced (424+/-52 vs. 345+/-65 fpm, P<0.01). In this group, a finding of an AFR above the mean value of the study population predicted AF relapse with high accuracy. CONCLUSION: In patients undergoing cardioversion of persistent AF, AF relapse is predicted by a higher AFR. A stronger association is seen in patients with short arrhythmia duration, reflecting either rapid remodelling or pre-existing changes in those who relapse to AF.

Adrenergic beta-Antagonists↗

PubMed2006

Atrial septal defect: a diagnostic approach.

A simple objective screening method for diagnosis of the atrial septal defect (ASD) is needed. Acoustic signals were collected from 61 children with ASD and 60 with a physiological murmur. The second heart sound (S2) and the spectrum of systolic murmur were analysed. A statistical model was designed using stepwise logistic regression analysis. Significant variables distinguishing pathological form normal findings were the interval between the first heart sound and the beginning of systolic murmur or the respiratory variation of S2, and the frequency of the murmur at its maximum intensity. The area under the ROC curve was 0.922; indicating very good fit of the model and the confidence interval was 0.872-0.971. The sensitivity of the model was 91% and the specificity 73%. The analysis of acoustic findings from the heart is a valuable tool in diagnosing ASD. The next step will be automating this process.

Adolescent↗

PubMed2006

Atrial fibrillation signal organization predicts sinus rhythm maintenance in patients undergoing cardioversion of atrial fibrillation.

AIMS: Electrical remodelling is believed to influence the outcome following cardioversion of patients with persistent atrial fibrillation (AF). However, the results in clinical studies are conflicting. We assessed the hypothesis that non-invasively obtained atrial fibrillatory organization can be used as a predictor of sinus rhythm (SR) maintenance. METHODS AND RESULTS: Fifty-four patients (37 men, age 67+/-11) with persistent AF (median duration 3 months, 1 day to 18 months), without anti-arrhythmic drug treatment, referred for cardioversion were studied. Assessment of the atrial harmonic decay was made by time-frequency analysis of the ECG. At 1-month follow-up, 30 patients had relapsed into AF. The mean harmonic decay at inclusion of those relapsing into AF was 1.5+/-0.3 compared with 1.1+/-0.3 among those maintaining SR (P=0.0004). Using a cut-off value of harmonic decay <or=1.5 to determine suitability for cardioversion would have resulted in a clinically useful discriminator (sensitivity=92%, specificity=47%, PPV=59%, and NPV=88%). CONCLUSION: This study shows that patients relapsing rapidly to AF have a higher harmonic decay than those maintaining SR. The degree of AF signal organization (harmonic decay) was a superior discriminator to other patient parameters. Further studies are needed to confirm these results and to determine the electrophysiological correlate of harmonic decay.

Aged↗

PubMed2006

Prediction of sinus rhythm maintenance following DC-cardioversion of persistent atrial fibrillation - the role of atrial cycle length.

BACKGROUND: Atrial electrical remodeling has been shown to influence the outcome the outcome following cardioversion of atrial fibrillation (AF) in experimental studies. The aim of the present study was to find out whether a non-invasively measured atrial fibrillatory cycle length, alone or in combination with other non-invasive parameters, could predict sinus rhythm maintenance after cardioversion of AF. METHODS: Dominant atrial cycle length (DACL), a previously validated non-invasive index of atrial refractoriness, was measured from lead V1 and a unipolar oesophageal lead prior to cardioversion in 37 patients with persistent AF undergoing their first cardioversion. RESULTS: 32 patients were successfully cardioverted to sinus rhythm. The mean DACL in the 22 patients who suffered recurrence of AF within 6 weeks was 152 +/- 15 ms (V1) and 147 +/- 14 ms (oesophagus) compared to 155 +/- 17 ms (V1) and 151 +/- 18 ms (oesophagus) in those maintaining sinus rhythm (NS). Left atrial diameter was 48 +/- 4 mm and 44 +/- 7 mm respectively (NS). The optimal parameter predicting maintenance of sinus rhythm after 6 weeks appeared to be the ratio of the lowest dominant atrial cycle length (oesophageal lead or V1) to left atrial diameter. This ratio was significantly higher in patients remaining in sinus rhythm (3.4 +/- 0.6 vs. 3.1 +/- 0.4 ms/mm respectively, p = 0.04). CONCLUSION: In this study neither an index of atrial refractory period nor left atrial diameter alone were predictors of AF recurrence within the 6 weeks of follow-up. The ratio of the two (combining electrophysiological and anatomical measurements) only slightly improve the identification of patients at high risk of recurrence of persistent AF. Consequently, other ways to asses electrical remodeling and / or other variables besides electrical remodeling are involved in determining the outcome following cardioversion.

Aged↗

PubMed2006

Comparison of ST-segment deviation to scintigraphically quantified myocardial ischemia during acute coronary occlusion induced by percutaneous transluminal coronary angioplasty.

This study compared ST-segment changes during acute coronary artery occlusion with measurements of ischemia by myocardial scintigraphy. Forty patients who were referred for elective prolonged percutaneous transluminal coronary angioplasty underwent 12-lead electrocardiographic recording before the procedure (baseline) and continuously during the entire balloon inflation (occlusion). For each patient, the summed ST-segment deviation was calculated as the maximal absolute difference, elevation or depression, between baseline and occlusion recordings in all 12 leads. Each patient underwent 2 myocardial scintigraphies, 1 with technetium-99m sestamibi injected during the balloon inflation and 1 on the following day as a control study. Ischemia that was induced by balloon occlusion was quantified in terms of extent and severity. Results for the entire study group showed that summed ST deviation correlated with extent (r = 0.59, p < 0.0001) and severity (r = 0.61, p < 0.0001) of ischemia. The location of maximal ST deviation differed for the 3 arteries. For occlusion of the left anterior descending artery, maximal ST deviation was elevated in lead V3. For occlusion of the left circumflex artery, maximal ST deviation was depressed in lead V2. Occlusion of the right coronary artery caused ST elevation in lead III and ST depression in lead V2. In conclusion, this study demonstrated a significant correlation between summed ST deviation and myocardial ischemia during coronary occlusion that is induced by percutaneous transluminal coronary angioplasty.

Acute Disease↗

PubMed2006

Predicting spontaneous termination of atrial fibrillation using the surface ECG.

By recognizing and characterizing conditions under which atrial fibrillation (AF) is likely to terminate spontaneously or be sustained, improved treatment of sustained AF may result and unnecessary treatment of self-terminating AF avoided. Time-frequency measures that characterize AF, such as fibrillatory frequency, amplitude, and waveform shape (exponential decay), are extracted from the residual ECG following QRST cancellation. Three complexity measures are also studied, characterizing the degree of organization of atrial activity. All measures are analysed using a training set, consisting of 20 recordings of AF with known termination properties, and a test set of 30 recordings. Spontaneous termination was best predicted by a low and stable fibrillatory frequency and a low exponential decay. Using these predictors, 90% of the test set was correctly classified into terminating and sustained AF. Neither fibrillation amplitude nor the complexity measures differed significantly between the two sets.

Algorithms↗

PubMed2006

Analysis of surface electrocardiograms in atrial fibrillation: techniques, research, and clinical applications.

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Neither the natural history of AF nor its response to therapy is sufficiently predictable by clinical and echocardiographic parameters. The purpose of this article is to describe technical aspects of novel electrocardiogram (ECG) analysis techniques and to present research and clinical applications of these methods for characterization of both the fibrillatory process and the ventricular response during AF. Atrial fibrillatory frequency (or rate) can reliably be assessed from the surface ECG using digital signal processing (extraction of atrial signals and spectral analysis). This measurement shows large inter-individual variability and correlates well with intra-atrial cycle length, a parameter which appears to have primary importance in AF maintenance and response to therapy. AF with a low fibrillatory rate is more likely to terminate spontaneously and responds better to antiarrhythmic drugs or cardioversion, whereas high-rate AF is more often persistent and refractory to therapy. Ventricular responses during AF can be characterized by a variety of methods, which include analysis of heart rate variability, RR-interval histograms, Lorenz plots, and non-linear dynamics. These methods have all shown a certain degree of usefulness, either in scientific explorations of atrioventricular (AV) nodal function or in selected clinical questions such as predicting response to drugs, cardioversion, or AV nodal modification. The role of the autonomic nervous system for AF sustenance and termination, as well as for ventricular rate responses, can be explored by different ECG analysis methods. In conclusion, non-invasive characterization of atrial fibrillatory activity and ventricular response can be performed from the surface ECG in AF patients. Different signal processing techniques have been suggested for identification of underlying AF pathomechanisms and prediction of therapy efficacy.

Atrial Fibrillation↗

PubMed2006

An efficient method for handling ectopic beats using the heart timing signal.

The problem of analyzing heart rate variability in the presence of ectopic beats is revisited. Based on the integral pulse frequency modulation model and the closely related heart timing signal, a new technique is introduced which corrects for the occasional presence of ectopic beats. The correction technique, which involves the occurrence times of a certain number of beats preceding the ectopic beat, is computationally very efficient. From actual heart rate data, the results show that the new technique is associated with a much lower computational complexity (flops reduced by a factor of about 3000) than the original heart timing technique, while producing similar performance. It is also shown that the power spectrum and related clinical indices obtained by the new technique are more accurately estimated than by other methods.

Algorithms↗

PubMed2006

Comparison of atrial signal extraction algorithms in 12-lead ECGs with atrial fibrillation.

Analysis of atrial rhythm is important in the treatment and management of patients with atrial fibrillation. Several algorithms exist for extracting the atrial signal from the electrocardiogram (ECG) in atrial fibrillation, but there are few reports on how well these techniques are able to recover the atrial signal. We assessed and compared three algorithms for extracting the atrial signal from the 12-lead ECG. The 12-lead ECGs of 30 patients in atrial fibrillation were analyzed. Atrial activity was extracted by three algorithms, Spatiotemporal QRST cancellation (STC), principal component analysis (PCA), and independent component analysis (ICA). The amplitude and frequency characteristics of the extracted atrial signals were compared between algorithms and against reference data. Mean (standard deviation) amplitude of QRST segments of V1 was 0.99 (0.54) mV, compared to 0.18 (0.11) mV (STC), 0.19 (0.13) mV (PCA), and 0.29 (0.22) mV (ICA). Hence, for all algorithms there were significant reductions in the amplitude of the ventricular activity compared with that in V1. Reference atrial signal amplitude in V1 was 0.18 (0.11) mV, compared to 0.17 (0.10) mV (STC), 0.12 (0.09) mV (PCA), and 0.18 (0.13) mV (ICA) in the extracted atrial signals. PCA tended to attenuate the atrial signal in these segments. There were no significant differences for any of the algorithms when comparing the amplitude of the reference atrial signal with that of the extracted atrial signals in segments in which ventricular activity had been removed. There were no significant differences between algorithms in the frequency characteristics of the extracted atrial signals. There were discrepancies in amplitude and frequency characteristics of the atrial signal in only a few cases resulting from notable residual ventricular activity for PCA and ICA algorithms. In conclusion, the extracted atrial signals from these algorithms exhibit very similar amplitude and frequency characteristics. Users of these algorithms should be observant of residual ventricular activities which can affect the analysis of the fibrillatory waveform in clinical practice.

Algorithms↗

PubMed2006

Wavelet-based event detection in implantable cardiac rhythm management devices.

This paper presents a novel event detector for implantable devices. The algorithm is based on a signal model which describes an event as a linear combination of basis functions. The linear combination involves two fundamental electrogram waveforms represented at different time scales. An efficient, low-complexity detector is developed using the dyadic wavelet transform with integer filter coefficients, and a generalized likelihood ratio test. The results show that reliable detection is obtained at an intermediate signal-to-noise ratio (SNR = 25 dB) for various common noise sources. In terms of probabilities of missed events and false alarms, an over-all performance of 0.7% and 0.1%, respectively, was achieved on electrograms corrupted by the different noise types at an intermediate SNR.

Algorithms↗

PubMed2006

A robust method for ECG-based estimation of the respiratory frequency during stress testing.

A robust method is presented for electrocardiogram (ECG)-based estimation of the respiratory frequency during stress testing. Such ECGs contain highly nonstationary noise and exhibit changes in QRS morphology which, when combined with the dynamic nature of the respiratory frequency, make most existing methods break down. The present method exploits the oscillatory pattern of the rotation angles of the heart's electrical axis as induced by respiration. The series of rotation angles, obtained from least-squares loop alignment, is subject to power spectral analysis and estimation of the respiratory frequency. Robust techniques are introduced to handle the nonstationary properties of exercise ECGs. The method is evaluated by means of both simulated signals, and ECG/airflow signals recorded from 14 volunteers and 20 patients during stress testing. The resulting respiratory frequency estimation error is, for simulated signals, equal to 0.5% +/- 0.2%, mean +/- SD (0.002 +/- 0.001 Hz), whereas the error between respiratory frequencies of the ECG-derived method and the airflow signals is 5.9% +/- 4% (0.022 +/- 0.016Hz). The results suggest that the method is highly suitable for analysis of noisy ECG signals recorded during stress testing.

Adult↗

PubMed2006

Multiscale detection of transient evoked otoacoustic emissions.

This paper presents a unified approach to multiscale detection of transient evoked otoacoustic emissions (TEOAEs). Using statistical detection theory, it is shown that the optimal detector involves a time windowing operation where the window can be estimated from ensemble correlation information. The detector performs adaptive splitting of the signal into different frequency bands using either wavelet or wavelet packet decomposition. A simplified detector is proposed in which signal energy is omitted. The results show that the simplified detector performs significantly better than existing TEOAE detectors based on wave reproducibility or the modified variance ratio, whereas the detector involving signal energy does not offer such a performance advantage.

Acoustic Stimulation↗

PubMed2006

Serial changes in the high-frequency ECG during the first year following acute myocardial infarction.

BACKGROUND: Previous studies have shown reduced high-frequency QRS components (HF-QRS) after acute myocardial infarction (MI). The purpose of this study was to investigate serial changes in HF-QRS during the first year following acute MI. METHODS: A total of 75 patients were included. Standard- and high-frequency ECGs were recorded on five occasions during the year following the MI (a few days after the MI, after 6 weeks, and after 3, 6 and 12 months). RESULTS: There was a statistically significant increase in HF-QRS during the follow-up year (P = 0.002). There were no significant differences in HF-QRS when comparing either the infarct location or the presence or absence of reperfusive therapy. Large differences in HF-QRS were observed, both intra-individually and inter-individually, during the year. CONCLUSIONS: There was a statistically significant increase in HF-QRS during the year following acute MI.

Aged↗

PubMed2006

Indices of electrical and contractile remodeling during atrial fibrillation in man.

BACKGROUND: Atrial electrical and contractile remodeling have been demonstrated to coincide during atrial fibrillation (AF) in experimental studies. We explored whether electrical and contractile remodeling correlate in man and explored its clinical implications. METHODS: Forty-nine patients with persistent AF were studied. Electrical remodeling was assessed noninvasively using spectral analysis to estimate the average fibrillatory rate (AFR). Atrial contractility was assessed by transesophageal echocardiography (TEE) measurement of left atrial appendage outflow velocity (LAAOV). RESULTS: The AFR was 403+/-43 fibrillations per minute (fpm) and the LAAOV was 0.27+/-0.14 m/s. A significant correlation was found between AFR and LAAOV (r=-0.47, P=0.001). In patients with a LAAOV>or=0.25 m/s, the AFR was 387+/-48 fpm compared to 419+/-31 fpm among patients with LAAOV<0.25 m/s (P<0.01). CONCLUSIONS: This study demonstrates that indices of electrical and contractile remodeling are strongly correlated in persistent AF in man. The interindividual overlap, however, is too large to allow predictions of LAAOV based on fibrillatory frequency alone.

Action Potentials↗

PubMed2005

High-resolution analysis of ambulatory electrocardiograms to detect possible mechanisms of premature ventricular beats.

For generations of electrocardiogram (ECG) analysis, the presence of premature ventricular beats (PVBs) has been characterized as a common event in the ECG without regard to the mechanism which has caused the PVB in the first place. At best, the coupling interval with the preceding sinus beat may be noted. This viewpoint persisted throughout the era of automated ECG analysis, as well as influencing the treatment of more life threatening events by PVB suppression strategies alone. This study proposed three hypotheses which would link the PVB to a specific mechanism or milieu. Each of these hypotheses requires significant signal processing of the continuously recorded high resolution ECG. Data are presented which demonstrate that abnormal intra-QRS potentials may be linked to a reentrant mechanism for the PVBs and that many patients have significant changes in these potentials in the sinus beats preceding the PVB. Changes in the characteristics of the repolarization as measured in the T/U wave period were also observed and could be linked to triggered activity mechanism for some PVBs. Finally, the role of subclinical ST segment changes also indicates that low grade ischemia may play a role in modulating either PVB mechanism. The data generated by this study suggest that a new view toward PVB mechanism as measured by ECG characteristics may warrant a more rational approach to renewed interest identifying the malignant PVBs and their eventual clinical management.

Algorithms↗